The present invention relates to postage meters (or "franking machines") in which the print head comprises a print drum carrying printwheels. More particularly, in such machines the invention relates to a device for locking the printwheels in position.
In conventional manner, printwheels are rotatably mounted on the drum so as to enable their positions to be adjusted, while they are not franking mail. In addition, they project slightly from the periphery of the drum and they are rotatable therewith for the purpose of printing both fixed and variable franking information for each revolution of the drum. The printwheels are used for printing variable information such as postage date and amount. The print drum thus carries two sets of printwheels for variable information, which wheels project from the drum through appropriate openings in a printing plate engraved with a postal flier. This engraved plate fits around the periphery of the drum and carries fixed postal information in the form of a print for the postage stamp proper and a print for the home post office, or for some other specified information. In general, the same drum also carries another engraved plate for advertising purposes which is analogous to the first but is often removably mounted, and which serves for printing unchanging advertising information. In some machines, other print means such as one or more removable blocks are associated with the drum.
For position adjustment purposes, the printwheels are generally coupled to a motor or to a manually driven control assembly having gear wheels referred to as driving gear wheels which, by means of respective drive systems serve to drive driven gear wheels on the printwheels. The motor-driven control assembly is then connected to a control card itself connected to data input means, e.g. a keypad and associated display screen on the machine.
Once adjustment has been performed, an object of the invention is to lock the racks and the printwheels on each printing cycle while they are rotating with the drum.
It is absolutely essential, and indeed legally required, to provide a device that hinders any attempt at changing the settings of the printwheels while the print drum is rotating.
Such locking devices already exist, and, by way of example of the prior art on this topic, mention may be made of French patent application FR-A-2 665 781, filed by the Applicant company on Aug. 7, 1990.